Lung deposited surface area in Leicester urban background site/UK: Sources and contribution of new particle formation

Sarkawt M.L Hama,Nan Ma,Rebecca L Cordell,Gerard P.A Kos,Alfred Wiedensohler,Paul S Monks

doi:10.1016/j.atmosenv.2016.12.002

Abstract

Lung Deposited Surface Area (LDSA) has been identified as a potential metric for the correlation of a physical aerosol particle properties with health outcomes. Currently, there is little urban LDSA data. As a case study, we investigated measurements of LDSA (alveolar) concentrations in a mid-size European city. LDSA and associated measurements were carried out over 1.5 years at an urban background site in Leicester, UK. Average LDSA concentrations in the cold (November–April) and warm (May–October) seasons of UK were 37 and 23 μm2 cm−3, respectively. LDSA correlates well (R2 = 0.65–0.7, r = 0.77–0.8) with traffic related pollutants, such as equivalent black carbon (eBC) and NOX. We also report for the first time in the UK the correlation between an empirically derived LDSA and eBC. Furthermore, the effect of wind speed and direction on the LDSA was explored. Higher LDSA concentrations are observed at low wind speeds (1–2 m s−1), owing to local traffic emissions. In addition, the diurnal variation of LDSA showed a second peak in the afternoon under warm and relatively clean atmospheric conditions, which can be attributed to photochemical new particle formation (NPF) and growth into the Aitken mode range. These NPF events increased the average background LDSA concentrations from 15.5 to 35.5 μm2 cm−3, although they might not be health-relevant. Overall, the results support the notion that local traffic emissions are a major contributor to observed LDSA concentrations with a clear seasonal pattern with higher values during winter.

Highlights

The surface area concentration is an important property of atmospheric aerosol particles which links aerosol loading to its health effects
lung deposited surface area (LDSA) concentrations and particle number size distributions (PNSD) have been measured in the Leicester urban atmosphere along with observations of equivalent black carbon (eBC), and NOx concentrations
The diurnal variation of LDSA concentrations observed can be rationalised in terms of the influence of traffic emissions and any dilution effects

Summary

Introduction

The surface area concentration is an important property of atmospheric aerosol particles which links aerosol loading to its health effects. Toxicological studies have found that ultrafine particles may have an increased toxicity compared to larger particles with the same composition (Johnston et al., 2000; Karlsson et al, 2009), and that the surface area concentration might be the most relevant physical measurement of ultrafine particle exposure (Maynard and Maynard, 2002; Moshammer and Neuberger, 2003; Oberdörster, 2000) All these studies reveal that the surface area concentration of atmospheric particles in various environments is a suitable property to represent the negative human health effects of aerosol exposure. Such instruments may offer the ability to explore source-related ultrafine particle exposure as they deliver high temporal and potentially spatially disaggregated measurements, which addresses requirements around the nature of ultrafine particles to coagulate quickly and create significant concentration gradients (Imhof et al, 2005; Peters et al, 2009). In these instruments a corona discharge produces unipolar ions, which can diffuse towards the particles and an electrometer is used to measure the total charge that transfers from the ions to the particles; the amount of charge is related to the active surface area concentration (Asbach et al, 2009; Baltensperger et al, 2001)

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